Study On Corrosion Resistance And Condensation Property Of Ni-P/Nano SiO₂ Composite Coatings

Electroless composite coatings are prepared by adding nanoparticles into plating bath. The incorporation of nanoparticles into Ni-P matrix can provide excellent functional properties. In this paper, Ni-P/Nano SiO2 composite plating was developed by co-depositing nano-sized power SiO2 during electroless plating, and its corrosion resistance and condensation property were investigated.Due to the fact that the composite plating bath is not stable and nanoparticles is difficult to scatter, the preparation process of Ni-P/Nano SiO2 composite coating was optimized in this paper, and its corrosion resistance was studied through immersion test and electrochemical corrosion test technology. The results showed that composite coatings were more dense than common Ni-P coating and it showed better corrosion resistance performance. It is found that composite coating corrosion rate decreased by 33.5% compared with common coating and was less than 10% of the corrosion rate of SS316 stainless steel by sulfuric acid dew point corrosion experiment.Condensation heat transfer characteristics of steam on vertical plates with Ni-P and Ni-P/Nano SiO2 platings were studied experimentally. The results showed that complete dropwise condensation heat transfer was formed on the coating surface. When the subcooling temperatures was 2.5 K, compared with film condensation, the heat transfer coefficient of common Ni-P coating was increased four times or so, Ni-P/Nano SiO2 composite coating surface increased nearly five times. The coating's amorphous structure coating was the main reason to promote dropwise condensation heat transfer form. When coatings were crystallized by heat treatment, their condensation heat transfer form were film and drops coexisted.